Enhancing reception of signals in global positioning system (GPS) receiver module

ABSTRACT

An antenna assembly for receiving the GPS signals in a global positioning system (GPS) receiver module automatically orients the antenna to better receive the GPS signals. The antenna is oriented by a positioner (e.g., a counterweight) that automatically rotates a frame on which the antenna is mounted. The GPS receiver module may also include multiple antennas oriented in different directions to maintain good reception of the GPS signals in any position. The multiple antennas are oriented in a manner so that the poor reception range an antenna is covered by other antennas. Signals from multiple antennas may be combined or chosen for processing by a GPS processor. Also, multiple GPS receiver modules may be deployed in close proximity so that wireless communication between the GPS receiver modules may be established.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims priorityunder 35 U.S.C. §121 to co-pending U.S. patent application Ser. No.12/013,860 entitled “Enhanced Reception of Signals in Global PositioningSystem (GPS) Receiver Module,” filed on Jan. 14, 2008, which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to enhancing the performance of a GlobalPositioning System (GPS) receiver module, and more particularly toenhancing reception of the GPS signals or using other information todetermine the location of a GPS receiver module.

2. Background of the Invention

Global Positioning System (GPS) is a multiple-satellite based radiopositioning system in which each GPS satellite transmits signals thatallow locations to be determined by measuring the distance from selectedGPS satellites. The satellites are positioned in a constellation suchthat typically seven, but a minimum of four satellites will beobservable by a user anywhere on or near the earth's surface. Therefore,the GPS satellites provide GPS signals that may be received globally ona continuous basis. The GPS signals are carried over two frequenciesknown as L1 (1575.42 MHz) and L2 (1227.6 MHz) using spread spectrumtechniques that employ spreading functions.

GPS is intended to be used in a wide variety of civilian and militaryapplications such as vehicle navigation, precise positioning, timetransfer, attitude reference, and surveying. FIG. 1 is a diagramillustrates an application of tracking parcels 122 transported via avehicle 120. GPS receiver modules are contained or secured to theparcels 122 to determine and track the location of the parcels 122 basedon the GPS signals from a constellation of satellites 110.

A GPS receiver module comprises a number of components including, amongother components, an antenna assembly, an RF assembly, and a GPSprocessor. The antenna assembly receives the L-band GPS signal and feedsit to the RF assembly. The RF assembly mixes the L-band GPS signal downto a signal of intermediate frequency (IF). Using various knowntechniques, the PRN code modulating the L-band signal is tracked throughcode-correlation to measure the time of transmission of the signals fromthe satellite. The GPS processor differences the measured time oftransmission with the time of reception and determines a pseudo rangebetween the receiver and the satellite. This pseudo range includes boththe range to the satellite and the offset of the receiver's clock fromthe GPS master time reference. The GPS processor computes a threedimensional position based on the pseudo range measurements andnavigation data from multiple satellites.

Reception of the GPS signals at the GPS receiver module is vital todetermining accurate location of the GPS receiver. For various reasons,however, the quality of GPS signals received at the GPS receiver modulemay be degraded. One of the causes of poor reception is the non-optimalorientation of the antenna. If the GPS antenna is not oriented towardthe satellites, the reception of the GPS signals may be poor. FIG. 2illustrates a graph illustrating an antenna pattern of a conventionalGPS antenna. The GPS antenna of FIG. 2 has good signal reception up toapproximately 100 degrees from the pattern maximum (at 0 degree) butdegrades significantly above approximately 100 degrees and reaches thepattern minimum at 180 degrees from the pattern maximum. In this rangebetween approximately 100 degrees and 180 degrees, the signal receptionis degraded significantly. If the GPS signals are received in this poorreception range, the reception of the GPS signals degradessignificantly. Although the reception may be improved by manuallyreorienting the GPS antennas so that the poor reception range does notface the satellites, the manual adjustment of the GPS antennas may notbe practicable or possible in some applications.

SUMMARY OF THE INVENTION

In one embodiment, reception of global positioning system (GPS) signalsis enhanced by automatically adjusting the orientation of an antenna ofa GPS receiver module. Specifically, an antenna assembly of the GPSreceiver module may include a directional antenna secured to a rotatingframe. The antenna is mounted on a rotatable frame that rotatesautomatically so that the poor reception range of the antenna does notface toward the source of the GPS signal (e.g., toward the sky). Theframe may be rotated by a positioner (e.g., a counterweight) secured tothe frame. By automatically adjusting the orientation of the antenna,good reception of the GPS antenna is maintained regardless of theposition or orientation of the GPS receiver module.

In one embodiment, reception of the GPS signals is enhanced by usingmultiple antennas oriented in different directions. At least one antennaof the two or more antennas has good reception of the GPS signals. TheGPS signals from the antenna with good reception can be tuned, decodedand processed. One antenna complements the poor reception range of otherantennas, and thus, at least one antenna provides the GPS signals ofgood quality. The GPS signals from the multiple antennas may be combinedto generate enhanced GPS signals. Alternatively, an antenna of apreferred orientation may be selected to provide the GPS signals forprocessing.

In one embodiment, the orientation of the antennas may be tracked toselect an antenna from multiple antennas to receive the GPS signals. Anaccelerometer detects the direction of earth's gravity and controls aswitch that selectively couples a location processor and the antennas.Specifically, the switch may couple the location processor to an antennathat is oriented toward the source of the GPS signals. By receiving theGPS signals via multiple antennas and selecting an antenna that hasbetter reception, the GPS receiver module can more accurately determineits location.

In one embodiment, the acceleration signal from the accelerometer islow-pass filtered to avoid frequent switching of the antenna. Highfrequency components of the acceleration signals may be caused bynoises, vibrations or transient motions to the GPS antenna assemblywhich may not reflect the true orientation of the GPS receiver module.The low-passed filtered acceleration signals have suppressed or reducedhigh frequency components compared to unfiltered acceleration signals,and thus, are more reflective of the actual orientation of the antennas.

The features and advantages described in the specification are not allinclusive and, in particular, many additional features and advantageswill be apparent to one of ordinary skill in the art in view of thedrawings, specification, and claims. Moreover, it should be noted thatthe language used in the specification has been principally selected forreadability and instructional purposes, and may not have been selectedto delineate or circumscribe the disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments disclosed can be readily understood by considering thefollowing detailed description in conjunction with the accompanyingdrawings.

FIG. 1 is a diagram illustrating parcels tracked using globalpositioning system (GPS).

FIG. 2 is a graph illustrating an antenna pattern of a GPS antenna.

FIG. 3 is a diagram illustrating a GPS receiver module having an antennaassembly with a rotatable frame, according to one embodiment.

FIGS. 4A to 4D are diagrams illustrating the GPS receiver module of FIG.3 placed in different orientations, according to one embodiment.

FIG. 5 is a diagram illustrating a GPS receiver module having twoantennas oriented in opposite directions, according to one embodiment.

FIG. 6 is a block diagram of an antenna assembly combining GPS signalsfrom two antennas, according to one embodiment.

FIG. 7 is a flowchart illustrating a method of enhancing reception ofthe GPS signals by combining the GPS signals from two antennas,according to one embodiment.

FIG. 8 is a block diagram of an antenna assembly switching between twoantennas to receive the GPS signals, according to one embodiment.

FIG. 9A is a graph illustrating an acceleration signal from anaccelerometer for switching the antennas, according to one embodiment.

FIG. 9B is a graph illustrating a low-pass filtered version of theacceleration signal of FIG. 9A, according to one embodiment.

FIG. 9C is a graph illustrating using hysteresis in the filteredacceleration signal to switch the antennas less frequently, according toone embodiment.

FIG. 9D is a graph illustrating selection of the antenna based on thefiltered acceleration signal of FIG. 9C, according to one embodiment.

FIG. 10 is a flowchart illustrating a method of switching the antennas,according to one embodiment.

FIG. 11 is a diagram illustrating a cluster of GPS receiver modulescommunicating with each other, according to one embodiment.

FIG. 12 is a block diagram illustrating the GPS receiver module of FIG.11, according to one embodiment.

FIG. 13 is an interaction diagram illustrating a method of sendinglocation information from a provider GPS receiver module to a client GPSreceiver module as initiated by the client GPS receiver module,according to one embodiment.

FIG. 14 is an interaction diagram illustrating a method of sendinglocation information from a provider GPS receiver module to a client GPSreceiver module as initiated by the provider GPS receiver module,according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The Figures (FIG.) and the following description relate to preferredembodiments of the present invention by way of illustration only. Itshould be noted that from the following discussion, alternativeembodiments of the structures and methods disclosed herein will bereadily recognized as viable alternatives that may be employed withoutdeparting from the principles of the claimed invention.

Reference will now be made in detail to several embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying figures. It is noted that wherever practicable, similar orlike reference numbers may be used in the figures and may indicatesimilar or like functionality. The figures depict embodiments of thepresent invention for purposes of illustration only. One skilled in theart will readily recognize from the following description thatalternative embodiments of the structures and methods illustrated hereinmay be employed without departing from the principles of the inventiondescribed herein.

GPS Receiving Module Having Antenna Assembly with Rotating Antenna Frame

In one embodiment, reception of global positioning system (GPS) signalsis enhanced by automatically adjusting the orientation of an antenna ofa GPS receiver module. Specifically, an antenna assembly includes adirectional antenna secured to a frame rotating automatically so thatthe poor reception range of the antenna does not face toward the sourceof the GPS signal. The poor reception range is the field of reception atthe antenna where the signal reception is degraded significantly. Byautomatically adjusting the orientation of the antenna, good receptionof the GPS antenna is maintained regardless of the position and/ororientation of the GPS receiver module.

FIG. 3 is a GPS receiver module 35 including an antenna assembly,according to one embodiment. The antenna assembly of FIG. 3 includes,among other components, a rotatable frame 30, a pivot 32 rotatablysecuring the rotatable frame 30, a directional GPS antenna 33, an arm36, two restrictors 34 a, 34 b, and a counterweight 38. The directionalantenna 33 and the counterweight 38 are secured to the frame 30. Thecounterweight 38 weighs more than the combination of the arm 36 and theantenna 33. In one embodiment, the frame is cylindrical in shape.

The counterweight 38 functions as the positioner that rotates the frame30 when the antenna assembly is placed in a vertically upright manner.The gravity (as indicated by an arrow 37) acts on the counterweight 38and forces the frame to rotate (e.g., counterclockwise in FIG. 3) sothat the pattern maximum of the directional antenna 33 orients towardthe source of the GPS signals (i.e., satellites). The pattern maximum ofthe directional antenna 33 is in the direction as illustrated by anarrow 31, while the pattern minimum is in the opposite direction. Thepattern maximum is a point in the antenna pattern where the signalreception is the best, and the pattern minimum is a point in the patternantenna where the signal reception is the worst. The signal reception inthe range around the pattern minimum is poor, and thus, the signalreception is degraded significantly if the GPS signals are received inthis poor reception range. In the example of FIG. 2, the poor receptionrange of the antenna is the range between approximately 100 degree and180 degrees from the pattern maximum at 0 degree. By rotating the frame30 so that the pattern maximum point of the directional antenna 33 headsupwards, the directional antenna 33 is automatically oriented to havegood reception of the GPS signals.

When the frame 30 is placed in a horizontal manner (i.e., the axis ofthe pivot 32 generally parallel to the arrow 37), the gravity does notact on the counterweight to rotate the frame 30. Referring to FIG. 2,however, the quality of reception of the GPS signals is generally goodor fair up to an angle of approximately 100 degrees from the patternmaximum (0 degree). Therefore, as long as the poor reception range doesnot face upwards to the satellites 110, the reception of the GPS signalsat the antenna 33 is acceptable without any rotation of the frame 30.

The arm 36 in conjunction with the restrictors 34 a, 34 b functions tolimit the rotation of the frame 30. By limiting the rotation of theframe 30, the pendulum motion of the frame 30 is prevented. The pendulummotion of the frame makes the reception of the GPS signals at thedirectional antenna 33 unstable, and should be avoided. In oneembodiment, the restrictors 34 a, 34 b and the arm 36 are removed toallow further rotation of the frame 30. A damper may be provided toreduce the pendulum motion of the frame 30.

FIGS. 4A to 4D illustrate the orientation of the antenna 33 in variousorientations of the GPS receiver module 35. As illustrated in FIGS. 4Ato 4D, regardless of how the antenna assembly is oriented, the antenna33 is oriented so that good reception of the GPS signals is maintained.By orienting the antenna 33 so that the poor reception range of theantenna 33 does not face the source of the GPS signals, the antenna 33can maintain good reception for the GPS signals in any positions andorientations of the GPS receiver module 35.

GPS Receiver Module Having Multiple Antennas

In alternative embodiments, the GPS receiver module includes multipleantennas oriented in different directions to maintain good reception ofthe GPS signals. The multiple antennas are oriented in a manner so thatthe poor reception range of one antenna is complemented or supplanted byother antennas. GPS signals from multiple antennas may be combined toobtain enhanced GPS signals, or one or more preferred antennas with goodsignal reception may be selected to provide the GPS signals forprocessing.

FIG. 5 is a diagram illustrating a GPS receiver module 50 including anantenna assembly with two antennas 56A, 56B oriented in oppositedirections (180 degrees), according to one embodiment. The antenna 56Ais oriented so that the poor reception range of the antenna 56B iscovered by the antenna 56A, and vice versa. The GPS signals from bothantennas 56A, 56B are fed to circuitry 52 for tuning, modulating, andprocessing of the GPS signals. The antennas need not be oriented inopposite directions; the two antennas may be oriented at any angle solong as the poor reception ranges of the two antennas do not overlap.

FIG. 6 is a block diagram of an antenna assembly enhancing GPS signalsby combining GPS signals from two antennas, according to one embodiment.The signal G_(SIG) _(—) _(A) received at the antenna 56A and the signalG_(SIG) _(—) _(B) are fed to circuitry 62. In one embodiment, theantenna 56A and the antenna 56B are oriented in the opposite direction.The circuitry 62 comprises a tuning circuit 64 and a combined output 66.The tuning circuit 64 includes a resistor-capacitor (RC) network 64including, among other components, a resistor R and capacitors C1, C2.The capacitors C1 and C2 are coupled in series. The resistor R iscoupled in parallel with the capacitors C1 and C2. The RC network 64filters and combines the GPS signals G_(SIG) _(—) _(A) and G_(SIG) _(—)_(B).

The enhanced GPS signal 68 is obtained at node 69 between the capacitorC1 and the capacitor C2. The enhanced GPS signal 68 is then fed to a GPSreceiver (not shown) connected to output 66. The GPS receiver (notshown) includes, among other components, a radio-frequency (RF)modulator and a GPS processor. The RF modulates the GPS signals into IF(Intermediate Frequency) signals to facilitate processing by the GPSprocessor. The GPS processor decodes and computes the location of theGPS receiver module based on the modulated GPS signals. The resistor andcapacitor network illustrated in FIG. 6 is merely illustrative, anddifferent combinations of resistors, capacitors or other electroniccomponents may also be used.

The antenna assembly of FIG. 6 is advantageous in that it includes onlypassive electronic components; and thus, does not consume power toenhance the GPS signals. Further, the antenna assembly of FIG. 6 issimple and inexpensive to implement.

FIG. 7 is a flowchart illustrating a method of enhancing the GPS signalsby combining GPS signals received at two antennas 56A, 56B, according toone embodiment. First, the GPS signal G_(SIG) _(—) _(A) is received 710at the antenna 56A. Likewise, the GPS signal G_(SIG) _(—) _(B) isreceived 712 at the antenna 56B. Then the GPS signals G_(SIG) _(—) _(A)and G_(SIG) _(—) _(B) are filtered 714 via the tuning circuit 64. TheGPS signals G_(SIG) _(—) _(A) and G_(SIG) _(—) _(B) are then combined718 at the tuning circuit 64, and provided 722 to the output 66. Theoutput 66 feeds the enhanced GPS signal to the GPS receiver whichmodulates, decodes, and processes the enhanced GPS signals to determine726 the location of the GPS receiver module.

FIG. 8 is a block diagram of an antenna assembly switching between twoantennas 56A, 56B to receive the GPS signals, according to oneembodiment. The antenna assembly of FIG. 8 includes, among othercomponents, two antennas 56A, 56B and circuitry 80. As in the embodimentof FIG. 6, the GPS signals G_(SIG) _(—) _(A) from the antenna 56A, andthe GPS signal G_(SIG) _(—) _(B) from the antenna 56B are fed to thecircuitry 80. The circuitry 80 in the embodiment of FIG. 8 is differentfrom the circuitry 62 of the embodiment of FIG. 6 in that the circuitry80 selectively couples the antennas 56A, 56B to the combined output 66using a switch 84. The circuitry 80 includes, among other components, asensor assembly 82, the switch 84, and the output 66.

The sensor assembly 82 generates and sends a switching signal S_(SW) toa switch signal node SW of the switch 84. The sensor assembly 82includes, among other components, an accelerometer 86, and a signalprocessing module 88. The accelerometer 86 generates an accelerationsignal indicating the orientation of the GPS receiver module by sensingthe direction of the gravity relative to the orientation of the GPSreceiver module. In one embodiment, a single-axis accelerometer is usedfor generating the acceleration signal indicative of the orientation ofthe accelerometer relative to Earth's gravity. In another embodiment, athree-axis accelerometer is used. For example, a single part digitalMEMS accelerometers (part no.: STM EK3LV02DQ) from ST Microelectronics(Geneva, Switzerland) may be used to generate the acceleration signal.This accelerometer is merely illustrative, and various otheraccelerometer may also be used.

The signal processing module 88 processes the acceleration signal fromthe accelerometer to generate the switching signal S_(SW), as describedbelow in detail with reference to FIGS. 9A to 9D.

The switch 84 receives the signal G_(SIG) _(—) _(A) at a first inputnode In1, and the signal G_(SIG) _(—) _(B) at the second input node In2.The switch 84 selectively couples the input nodes In1 and In2 with anoutput node Out of the switch 84 in accordance with the switching signalS_(SW). Therefore, depending on the switching signal S_(SW), either thesignal G_(SIG) _(—) _(A) or G_(SIG) _(—) _(B) (but not both) is providedto the GPS receiver (not shown) via the output 66 for tuning,modulation, decoding, and computation to determine the location of theGPS receiver module. By selecting one antenna and coupling the antennawith the output 66, the GPS receiver (not shown) receives GPS signalsG_(SIG) _(—) _(A) or G_(SIG) _(—) _(B) having better quality. The GPSsignals from one antenna are isolated from the GPS signals from theother antenna. Therefore, the GPS signals of high quality are notdegraded or corrupted by the GPS signals of lower quality before beingprovided to the GPS receiver.

FIG. 9A is a graph illustrating an acceleration signal from theaccelerometer 86, according to one embodiment. A high accelerationsignal represents that the GPS receiver module is oriented in adirection so that the antenna 56A has better reception of the GPSsignals than the antenna 56B. In contrast, a low acceleration signalrepresents that the GPS receiver module is oriented in a direction sothat the antenna 56B has better reception of the GPS signals than theantenna 56A.

The acceleration signal from the accelerometer 86 fluctuatessignificantly over time because the accelerometer 86 senses and changesthe acceleration signal according to transient dynamic motions of theGPS receiver module, noises and vibrations. Such short term dynamicmotions, noises and vibrations may not represent the true orientation ofthe GPS receiver module, and may lead the accelerometer 86 to generatethe acceleration signal not coinciding with the actual orientation ofthe GPS receiver module. Therefore, the acceleration signal from theaccelerometer is low-pass filtered as illustrated in FIG. 9B. When thefiltered acceleration signal is above a threshold, one antenna (e.g.,the antenna 56A) is selected to provide the GPS signals (e.g., G_(SIG)_(—) _(A)) to the GPS receiver (not shown) via the output 66. Incontrast, when the filtered acceleration signal is not above thethreshold, the other antenna (e.g., 56B) is selected to provide the GPSsignals (e.g., G_(SIG) _(—) _(B)) to the GPS receiver (not shown) viathe output 66.

In one embodiment, hysteresis is introduced in switching of the antennas56A, 56B. If the antennas for receiving the GPS signals are switchedfrequently, the GPS receiver module may lose track of the GPS signalsfrom the satellites and fail to track its current location. Byintroducing the hysteresis in the switching of the antennas 56A, 56B,frequent switching of the antennas 56A, 56B is suppressed. FIGS. 9C and9D are graphs illustrating selection of the antenna 56A, 56B based onthe filtered acceleration signal. In the example of FIGS. 9C and 9D, twodifferent levels of thresholds (high threshold and low threshold) servesas switching points of the switching signal S_(SW).

When the filtered acceleration signal is high and the antenna 56A isoriginally selected as illustrated in FIG. 9D, the switching to theantenna 56B does not occur until the filtered acceleration signal dropsbelow the low threshold. Note that the switching to the antenna 56B doesnot occur when the filtered acceleration signal drops below the highthreshold set at a level higher than the low threshold. After switchingto the antenna 56B, however, the switch 84 does not switch to theantenna 56A until the filtered acceleration signal rises above the highthreshold. Note that the switching to the antenna 56A does not occurwhen the filtered acceleration signal rises above the low threshold.That is, the switching point (e.g., the low threshold) at which theselected antenna switches from a first antenna (e.g., the antenna 56A)to a second antenna (e.g., the antenna 56B) is lower than the switchingpoint (e.g., the high threshold) at which the selected antenna switchesfrom the second antenna (e.g., the antenna 56B) to the first antenna(e.g., the antenna 56A). Similarly, the switching point (e.g., the highthreshold) at which the selected antenna switches from the secondantenna (e.g., the antenna 56B) to the first antenna (e.g., the antenna56A) is higher than the switching point (e.g., the low threshold) atwhich the selected antenna switches from the first antenna (e.g., theantenna 56A) to the second antenna (e.g., the antenna 56B).

By differentiating the switching point to and from one antenna to theother antenna, hysteresis is introduced in the switching of the antennas56A, 56B. In this way, the switching between the antennas 56A, 56Boccurs less frequently. The less frequent switching allows the GPSreceiver module to track its location more stably.

FIG. 10 is a flowchart illustrating a method of switching the antennas56A, 56B, according to one embodiment. First, the acceleration (i.e.,the direction of gravity relative to the orientation of the GPS receivermodule) is sensed 1010 at the accelerometer 86 to generate theacceleration signal. The acceleration signal is then filtered 1014 bythe signal processing module 88 to remove high frequency components ofthe acceleration signal. Then it is determined 1018 whether thecurrently selected GPS antenna is the antenna 56A or the antenna 56B. Ifthe currently selected antenna is the antenna 56A, the process proceedsto determining 1022 whether the filtered acceleration signal is abovethe high threshold.

If the filtered acceleration signal is above the high threshold, theantenna for receiving the GPS signals is switched 1026 to the antenna56B. Then the process proceeds to determine 1038 the location of the GPSreceiver module using the GPS signals from the antenna 56B. If thefiltered acceleration signal 1022 is not above the threshold at step1022, the selected antenna (i.e., the antenna 56A) remains unchanged.Then the process proceeds to determine 1038 the location of the GPSreceiver module using the GPS signals from the antenna 56A.

If the antenna currently selected is the antenna 56B (as determined atstep 1018), it is determined 1028 whether the filtered accelerationsignal is below the low threshold. If the filtered acceleration signalis below the low threshold, the process proceeds to switch 1030 theselected antenna to the antenna 56A. Then the process proceeds todetermine 1038 the location of the GPS receiver module based on the GPSsignals received from the antenna 56A. On the other hand, if it isdetermined (step 1028) that the filtered acceleration signal is notbelow the low threshold, the selected antenna (the antenna 56B) remainsunchanged. Then the process proceeds to determine 1038 the location ofthe GPS receiver module based on the GPS signals received at the antenna56B.

After determining 1038 the location of the GPS receiver module, theprocess returns to sensing 1010 the acceleration and generating theacceleration signal at the accelerometer 86.

Although the method of switching between antennas was described usingtwo antennas, alternative embodiments may include three or moreantennas. In one embodiment, two or more accelerometers are employed todetermine vertical acceleration and horizontal acceleration. In anotherembodiment, two or more accelerometers are placed in planes that areorthogonal to each other.

Cluster of GPS Receiver Modules

In alternative embodiments, multiple GPS receiver modules may bedeployed for tracking and determining the location of the GPS receivermodules. The multiple GPS receiver modules may be located in closeproximity so that wireless communication between the GPS receivermodules may be established. If the quality of the GPS signals receivedat the GPS receiver module is not above a threshold, the GPS receivermodule receives location information from other GPS receiver modules.The location indicated in the location information may then be taken asthe GPS receiver module receiving the location information or furtherprocessing may be performed on the location information to moreaccurately determine the location of the GPS receiver module receivingthe location information.

FIG. 11 is a diagram illustrating a cluster of GPS receiver modules1102-1112 deployed in an area. Each GPS receiver modules 1102-1112 maybe placed in different locations and/or conditions which causes thereception of the GPS signals to differ among the GPS receiver modules1102-1112. In the example of FIG. 11, three GPS modules (GPS modules1102, 1110, 1112) have poor reception of the GPS signals (represented by“−” mark), two GPS modules (GPS modules 1104, 1114) have good receptionof the GPS signals (represented by “+” mark), and the remaining GPSmodules (GPS modules 1106, 1108) may have no reception of the GPSsignals (represented by “X” mark).

The GPS receiver modules sending the location information is referred toas a “provider GPS receiver module.” The counterpart GPS receiver modulereceiving the location information is referred to as a “client GPSreceiver module.” In FIG. 11, the GPS module 1102 is illustrated as aclient GPS receiver module, and the GPS module 1104 is illustrated as aprovider GPS receiver module.

The provider GPS receiver module sends the location information to theclient receiver module upon the request from the client receiver moduleor after detecting a triggering event (e.g., passing of time).

After receiving the location information from the provider GPS receivermodule, the client GPS receiver module may take the location indicatedin the location information as its location. Alternatively, the clientGPS receiver module may receive the location information from multipleprovider GPS receiver modules, and perform triangulation or otherconventional techniques to compute or verify its location.

In one embodiment, a quality indicator is generated and transmitted bythe provider GPS receiver module. The quality indicator represents thequality of the GPS signal reception. The quality indicator may indicate,for example, the number of satellites from which the GPS signals werereceived. The client GPS receiver module may receive the locationinformation and the quality indicators from multiple provider GPSreceiver modules. The client GPS receiver module may use the locationinformation obtained from the provider GPS receiver module with thehighest quality indicator to determine the location of the client GPSreceiver module.

In one embodiment, the client GPS receiver module determines itslocation based on the GPS signals received at the GPS receiver modulewhen the quality of the GPS signals it received is above a predeterminedthreshold. If the quality of the received GPS signals is not above thepredetermined threshold, the client GPS receiver module may request theprovider GPS receiver to provide the location information and thequality indicator. The client GPS receiver module may compare thequalities of the GPS signals received at the client GPS receiver moduleand the provider GPS receiver module using the quality indicatorreceived from the provider GPS receiver module.

In one embodiment, after comparing the qualities of the received GPSsignals, the client GPS receiver module computes its location using theGPS signals received at the client GPS receiver module if the quality ofthe GPS signals received at the client GPS receiver module is betterthan the quality of the GPS signals received at the provider GPSreceiver module. In contrast, the client GPS receiver module uses thelocation information from the provider GPS receiver modules if thequality of the GPS signals received at the provider GPS receiver moduleis better than the GPS signals received at the client GPS receivermodule.

FIG. 12 is a block diagram illustrating the GPS receiver module 1210 ofFIG. 11, according to one embodiment. The GPS receiver module 1210includes, among other components, an antenna assembly 1212, a locationprocessor 1216, and a communication module 1220. The antenna assembly1212 is coupled to the location processor 1216. The communication module1220 is coupled to the location processor 1216.

The antenna assembly 1212 receives the GPS signals from the GPSsatellites and feeds the GPS signals to the location processor 1216. Anyone of the antenna assembly 1212 as described above with reference toFIGS. 3, 5, 6, and 8 or other conventional antenna assembly may be usedas the antenna assembly 1212.

The communication module 1220 is a short-range wireless communicationmodule (e.g., IEEE 802.15.4, Bluetooth, Wireless Fidelity (WiFi)component) capable of sending or receiving the location informationand/or the quality indicator. In one embodiment, the communicationmodule 1220 employs IEEE 802.15.4 physical standard. For example, thecommunication module 1220 may be implemented by Chipcon CC2420 radiocomponent from Texas Instrument (Dallas, Tex.) or Atmel RF 230 radiocomponent from Atmel Corporation (San Jose, Calif.) to communicate usingthe IEEE 802.15.4 physical standard in the 2.4 GHz ISM band. Thesecomponents are merely illustrative, and various other components mayalso be used. When the GPS receiver module 1210 is functioning as aprovider GPS receiver module, the communication module 1220 receives thelocation information and the quality indicator from the locationprocessor 1216 and transmits the location information and the qualityindicator to a client GPS receiver module wireless communication. Incontrast, when the GPS receiver module 1210 is functioning as a clientGPS receiver module, the communication module 1220 receives wirelessmessage including the location information and the quality indicatorfrom the provider GPS module and relays the message to the locationprocessor 1216.

The location processor 1216 determines the location of the GPS receivermodule 1210 based on either the GPS signals received via the antennaassembly 1212 or the location information received via the communicationmodule 1220. The location processor 1216 includes, among othercomponents, an RF modulator and a GPS processor (not shown). The RFmodulator modulates the GPS signal received via the antenna assembly1212 into modulated GPS signals for processing by the GPS processor. TheGPS processor decodes and processes the GPS signals to compute thelocation of the GPS receiver module 1210.

In one embodiment, the location processor 1216 extracts the qualityindicator from the message received from the provider GPS receivermodule and compares the quality of signal reception at the provider GPSreceiver module with the quality of GPS signals received via its antennaassembly 1212. The location processor 1216 determines the location ofthe GPS receiver module 1210 based on the GPS signals received via theantenna assembly 1212 if the quality of signal received via the antennaassembly 1212 is better than the quality of the GPS signals received atthe provider GPS receiver module. On the other hand, if the quality ofthe GPS signals received at the provider GPS receiver module is betterthan what is received via the antenna assembly 1212, the locationprocessor 1216 takes the location as indicated by the locationinformation as its location or performs processing based on the receivedlocation information.

By communicating with other GPS receiver modules to determine thelocation, the location of the GPS receiver module can be accuratelydetermined even if the reception of the GPS signals is not good oravailable at the GPS receiver module. Also, the location determinationmay become more robust because the location may be tracked even when thecomponents for tracking the GPS signals fail or malfunction.

The communication of the location information and/or the qualityindicator may be initiated either by a client GPS receiver module or aprovider GPS receiver module. FIG. 13 is an interaction diagram for oneembodiment in which the communication is initiated by the client GPSreceiver module 1102. First, the client GPS receiver module 1102broadcasts 1314 a request message M_(REQ) to other GPS receiver modules1106 for the location information when the GPS signal received at itsantenna assembly is not above a predetermined threshold. The providerGPS receiver module 1106 receives 1316 the request M_(REQ), and thengenerates 1318 the location information and the quality indicator basedon the GPS signals received at the provider GPS receiver module 1106.The provider GPS receiver module 1106 then transmits 1320 the locationinformation and the quality indicator to the client GPS receiver modulein a response message M_(RSP). The client GPS receiver module 1102collects 1322 the response message M_(RSP) from the provider GPSreceiver module 1102, and then computes its location 1324 by taking thelocation indicated in the location information as the location of theclient GPS receiver module 1102 or performing further processing (e.g.,triangulation) to determine more accurate location of the client GPSreceiver module 1102.

In one embodiment, the client GPS receiver module 1102 compares thequality of the receive GPS signals at the client GPS receiver module1102 and the provider GPS receiver module 1106. The client GPS receivermodule 1102 computes its location based on the location information whenthe GPS signal received at the provider GPS receiver module 1106 hasbetter quality compared to the GPS signals received at the client GPSreceiver module 1102. But the client GPS receiver module 1102 computesits location based on the GPS signals received at its antenna assembly1212 when the quality of the GPS signals received at its antennaassembly 1212 is better than the quality of the GPS signals received atthe provider GPS receiver module 1106.

FIG. 14 is an interactive diagram illustrating a method in which theprovider GPS receiver module 1106 periodically broadcasts the locationinformation regardless of requests from other GPS receiver modules. Inthis embodiment, the provider GPS receiver module 1106 generates 1412the location information and the quality indicator. Then the providerGPS receiver module 1106 broadcasts the location information and thequality information in a broadcast message M_(BRD). The client GPSreceiver module 1102 listens to and receives 1416 the broadcast messageM_(BRD) transmitted by the provider GPS receiver module 1106. Then theclient GPS receiver module 1102 computes 1418 the location of the clientGPS receiver module 1102 based on the location information received fromthe provider GPS receiver module 1106.

As in the embodiment of FIG. 10, the client GPS receiver module 1102 mayuse the location information when the GPS signal received at theprovider GPS receiver module 1106 is of better quality than the GPSsignals received at the client GPS receiver module 1102 but not when theGPS signal received at its antenna assembly 1212 is of better qualitythan the GPS signals received at the provider GPS receiver module 1106.

In one embodiment, the GPS receiver module 1102 may perform otherfunctions in addition to determining and tracking of its locations. Forexample, the GPS receiver module 1102 may monitor the temperature orhumidity of the surrounding environment.

While particular embodiments and applications have been illustrated anddescribed, it is to be understood that the present invention is notlimited to the precise construction and components disclosed herein andthat various modifications, changes and variations may be made in thearrangement, operation and details of the method and apparatus of thepresent invention disclosed herein without departing from the spirit andscope of the invention as defined in the appended claims.

1. An antenna assembly in a global positioning system (GPS) receivermodule, the antenna assembly comprising: a first antenna receiving GPSsignals, the first antenna having a first direction of maximum signalreception; a second antenna receiving the GPS signals, the secondantenna having a second direction of maximum signal reception, thesecond direction different than the first direction; an accelerometerfor generating an acceleration signal indicative of an orientation ofthe GPS receiver module; and a switch for selectively coupling the firstantenna or the second antenna with a location processor for processingthe GPS signals, the switch coupling the location processor with thefirst antenna responsive to the acceleration signal indicating that thefirst direction is aligned to a source of the GPS signals closer thanthe second direction, the switch coupling the location processor withthe second antenna responsive to the acceleration signal indicating thatthe second direction is aligned to the source of the GPS signals closerthan the first direction.
 2. The antenna assembly of claim 1, furthercomprising a signal processor between the accelerometer and the switchfor low-pass filtering the acceleration signal.
 3. The antenna assemblyof claim 1, wherein the switch couples the first antenna to the locationprocessor after the location processor is coupled to the second antennaresponsive to the acceleration signal dropping below a first threshold,the switch coupling the second antenna to the location processor afterthe location processor is coupled to the first antenna responsive to theacceleration signal exceeding a second threshold level higher than afirst threshold level.
 4. The antenna assembly of claim 1, wherein thefirst antenna and the second antenna are oriented in oppositedirections.